Japanese Patent No. 4665638 discloses a balancer device for an internal combustion engine connected to an oil pump. A torque from a crankshaft is input to a drive unit fixed to one end of a drive balancer shaft and transmitted to one end of a driven balancer shaft through a balancer drive gear and a balancer driven gear. The torque input to the driven balancer shaft is transmitted to the oil pump through a drive mechanism provided on the other end of the driven balancer shaft.